1. Field of the Invention
The present invention relates to a liquid crystal panel for use in a display apparatus.
2. Description of Related Art
Liquid crystal display apparatuses have been recently developed in various research institutes. Among the liquid crystal display apparatuses, a liquid crystal display mode called an "electric field controlled birefringence mode" has been known. This mode is characterized in that a liquid crystal is sandwiched between a pair of polarizers having a polarization axis orthogonal to each other, and the amount of birefringence in the liquid crystal is controlled by an applied electric field.
This electric field controlled birefringence mode has dispersion in the amount of transmitted light in connection with the wavelength of light, and therefore, a black indication cannot be obtained. However, a liquid crystal panel has been reported which has succeeded in cancelling the dispersion due to the wavelength so as to enable the black indication, by stacking two parallel-oriented liquid crystal cells so as to have the direction of orientation orthogonal to each other (SAITO and TAKAHASHI, "Non-colored indication by compensated homogeneous-oriented nematic (CHOC) LCD", Transaction of the 37th lecture of the Society of Applied Physics, page 806). If the two liquid crystal cell layers have the same value of .DELTA.n, a phase difference caused by one of the two liquid crystal cell layers can be returned to an original condition by the other liquid crystal cell layer. Therefore, the dispersion due to the wavelength can be compensated.
However, the above mentioned liquid crystal cell has large dependency of visual angle. Therefore, if the liquid crystal cell is observed from an inclined direction, it becomes difficult to recognize an image indicated in the liquid crystal cell.
This problem will be explained with reference to FIGS. 1A and 1B. In FIG. 1A, only one liquid crystal cell is shown for simplification of illustration. A homogeneous-oriented liquid crystal cell as shown in FIG. 1A is formed by fixing a pair of parallel-orienting substrates 10 and 12 in parallel to each other and to have a spacing therebetween, and filling a liquid crystal material 14 into the spacing between the pair of parallel-orienting substrates 10 and 12. The amount of birefringence is determined by an angle formed between an incident light ray and a long axis of the liquid crystal molecule. The larger the angle between the incident light ray and the long axis of the liquid crystal molecule becomes, the larger the amount of birefringence becomes, and the smaller the angle between the incident light ray and the long axis of the liquid crystal molecule becomes, the smaller the amount of birefringence becomes. Therefore, as shown in FIG. 1A, an incident light ray 16 in a direction perpendicular to or normal to the parallel-orienting substrates 10 and 12 will have a maximum amount of birefringence, and incident light rays 18A and 18B in a direction inclined to the normal direction of the parallel-orienting substrates 10 and 12 will have a decreased amount of birefringence.
FIG. 1B is a graph illustrating the above mentioned relation between the incident angle of light ray and the amount of birefringence. As seen from FIG. 1B, the homogeneous-oriented liquid crystal cell has the amount of birefringence varying greatly dependently upon a change of visual angle. This problem of dependency of the visual angle will become remarkable particularly in the case of a large-size display screen.